fahrenwald



g 9 a Apu.; 5 927 F. A. FAHRENWALD E @234@ METALLURG ICAI; FURNACE Filed 0G13. l2. 1925 Il, l /1 4Frmk A, Fahrenwdld Inventor 4 Y y @I April s; 1927.

F. A. FAHRENWALD METALLURG ICAL FURNACE www@ Filed Oct. 12. 1925 2 Sheets-Sheet 2 i rank A Fahre-nwald [n F fzzrfezzoz Patented Apr. 1927.

UNETE STATES PATENT @Ffii FRANK A. FAHRENWALD, OF CHICAGO HEIGHTS, ILLNOIS.

METALLURGIGAL FURNACE.

Application filed October l2, 1925.

This invention relates Ato metallurgical. furnaces of the type employed for the annealingof steel sheets und the heating or reheating of rods, rails, sheets, skelp, blooms, bars, and other articles during the process of rolling o1' forging. Ithas for its objects the provision of a new and improved construction of the furnace and roll whereby such sheets and other finished products can be annealed and the other articles can be heated with greater rapidity, less expense and better physical results than heretofore Formerly steel sheets were annealed by placing them in piles on suitable supports in a chamber which was afterwards heated and allowed to cool, it being considered impossible to transport the hot sheets. Later attempts were made to pass the sheets through a furnace in a continuous manner but difficulty was experienced in se curing satisfactory results, the difhculties experienced being mainly due to contact with the carrying members. These dithculties have been of two natures: first, a failure of the carrying members to reach the annealing temperature has resulted in lack of uniformity in the nished product; and also the surfaces of the sheets were blemished and marred by the supporting members which were either of greater hardness than the steel sheets at the temperature employed or which had hardened accretions built up thereon.

The maximum annealing temperature ever reached by the stationary process was seldom above 1700O Fahrenheit; the maximum temperature reached during the continuous process annealing has .seldom heretofore been above 1750". However, I have discovered that if a temperature of 1900o Fahrenheit can be obtained some vcry marked advantages are secured, chief among the saine being that the quick, sharp heating aords a maximum of softness and the quickness with which the heat-ing takes place also prevents grain growth and therefore results in a tine-grained, easily manipulated product. This high temperature, however, entails certain pronounced difficulties, chiefly concerned with the supporting of the sheets. For example, the sheets must be kept in rapid motion throughout the high temperature zone and I have further discovered that for the best results it is neces- Sary to have the supporting members hotter Serial No. 61,989.

than the sheets. Heretofore, owing to the necessity of shielding the supporting members7 the same were either mounted in a separate chamber having only their engaging portions projecting into the heated space, or elaborate water cooling precautions were employed which in either case so reduced the temperatures of the sheet-engaging portions as to prevent the portions of the steel sheets coming in contact therewith from reaching the same temperature as other portions and hence producing a sheet insuliicient in uniformity of text-ure and one which could not be drawn accurately to shape in dies; and in addition the oxide coating formed upon the sheet as a result of the heating becomes somewhat sticky at the annealing temperatures and is picked up by the colder supports where it forms irregular accretions which at their comparatively low temperature are so hard and sharp as seriously to dent and mar the heat-softened sheets with the result that smoothly finished work was ditiicult or impossible to obtain.

l have found if the rolls, or particularly the rims thereof, or other engaging members be kept at a temperature at least equal to or preferably above Athe temperature of the sheets, these drawbacks are entirely overcome. The sheets exhibit a high degree of uniformity in hardness and ductility and in the rare case that any oxide coating collects upon the rolls or rims or other supports it is comparatively soft and non-injurious at this high temperature, but the usual experience is that no such accumulation occurs inasmuch as this material appears to have a greater adhesion to the colder surface than to the warmer surface, with the result that it remains upon the sheet which is the cooler of the two. lt should be understood that the rolls are themselves made of a non-corrodible metallic a-lloy which does not itself oxidize under the conditions of operation and any oxide which may be present is that formed upon the surface of the sheet which is undergoing treatment and is transferred to the roll mechanically during the moment of Contact. In fact it is entirely possible by the use of suitable precautions, in combination with the improvements herein described, to effect this annealing in a neutral or reducing atmosphere.

In order to withstand the high temperatures employed in this operation and also to enable successful mounting-in :bearings I have found it important to make the rolls not only of a high temperature alloy but also of a peculiai'sliape and construction. In the drawings accompanying and forming a part of this application l have shown certain physical forms in Vwhich -my yinventive idea may be embodied although it will 4be understood that .many other `detail .forms can be devised and that these .drawings are intended rather to `illustrate `the general features of my invention -tl1an;to limit me vto the details shown. Fig. 1 is a `vertical cross sectional view through a furnace embodying ymy iimprovements showing one of my im-plv'oved .rolls partly in section and partly in elevation; Fig. 2 is a similar-view showinga modified type of'roll and bearing; Fig isla horizontal sectional View through a series of rolls showing a dif- Vferent type of roll; and Fig. 4 illustrates the preferred method of driving therolls.

vrEhe furnace itself preferably comprises a horizontal hearth 1, upright v.side Avalls2`2 and arche-droof-3 tlie .Walls being embrwed -by ,upright steel lI-beams' 4-4 and longitudinal members, certain of which are indicated at 5, 5, riveted thereto, thereby with :the assistance of further framing members, y'not shown, producing a frame .work which supports the thrust of' the roojfand steadies the side Walls.

`Secure-d to the ,uprights 1 -,et are horizontal shelves .6, 6, one at cachside of ythe furnace. on which areqmountedthe `journal Vboxes I7, 7 in` Whichare mounted the bearing portions 8, 8 ofthe rolls. ,Eaclnof these rolls comprises afhollow body `portion 10 having a dian'ieter considerably greater ,than ,that yof the shaft.l lPreferably Vthis body is east alliin onepiece vand 'integral with the lportions 8, 8 vthe latter bei-ng preferably hollow as shown in Figs. 1 and 3 although it is possible to make them solid;y as shown at `SiEl .in Fig. 2. There are numerous advantages vin making .these bearing portions hol'- loW; -the ,chief advantages being that it `re- .duces the conduction of heagt from ythe furnace interior, and that it facilitates supporting the core duringthe casting and the .breaking out ofl that core atter ,the gasting is effected. The body ofthe roll also is preferably formed with apertures 12, 12 cored therein. These apertures are best formed ,inthe `tapering ends vWhere the body of the roll joins the shaft although they may also be made inl the cylindrical portion ofi" the body, particularly ,incase theexteriorof the body. be formed with circumferential. ribs as indicated at 13 in Fig. 1, in` which case some of these apertures may fallbetween ad jacent ribs. These apertures have the combinel .affectyof Ikconstituting additional su ports for the core and of reducing the Weig t of the roll without seriously impairing its strength. The apertures in the slanting end portions have the further advantage of cutting down the amount of metal at this point andlhereby vreducing the cross section of metal available for the conduction of heat to the exterior of the furnace.

The-exterior of the roll may either be cylindrical and unbroken as shown in Fig. 3,'orvcylindrical andy apertnred as shown in F 1g. 2, or ribbed as shown in iFig. 1. Each fm'inationhas advantages. The smooth eX- tcrior ofthe'i-'olls in-Figs. 2 and 3 affords a lz'rige1';1.i'ea of Contact lfor the vilates, assuming the plates are sufficiently Vator flexible to Vlie smoothly, although it is necessary to smooth or grind a larger surface of roll; theuse oil ribs .13 as shown yin Fig. 1 reduces the amountof vroll surface necessary to be machined, but likewise reduces the area of possible cont-act -with the sheets.

AIt is-possibleto usethese rolls either naked as shown in Figs. 2 and 3 and at the right hand sidefof Fig. 1, or to provide them with circular lhoops or rims 15 of suitable alloy secured thereon in any suitable manner Aas shown at the left hand vside of Fig'. l. An advantage .of using these enlargements is Athatthe enlargements of adjacentrolls may interdit, thereby enabling a more uniform support o f the sheet ywith a larger space between adjacent rolls. Vhen these rims are Vused I preferito employ the ribbed type of ,roll `exterioras shown in Fig. 1. i

The .bearings may .be oit' numerous types .hut in any `case are preferably made of ,a .rather massive l.me-tal construction vintimate- ,especially high. Y

Any suitable or desired expedient ,may 4be .employed to rotate .these Vrolls but the one lprefer .is that shown in Figs. 1 3, and 4 wherein the end oit. each shaft is provided with a sheave 2,1 having. a peripheral groove 22 for the ,reception bf a cable 23. i This groove is prefer-ably made sufficiently Wide to ltake tn'o turns of cable, and the cable is preferably Wrapped around the sheaves so as `to exhibit a large area of frictional contact with each. Preferably this cable is wral'nied around the sheaves in pairs `as shown in Figs. 3 and 4. The Cable is 'kept `taut ,by'a suitable idler vpulley 24 and moved bya drive pulley 25. The advantage of this cable drive is ,that it is stead-y, uniform and very flexible. When gears are used there is llU necessarily a small degree of ine-qualityof motion, especially with the rather coarse toothed gears necessarily employed about such a furnace. As a result gearedrrolls do not all rotate evenly together but differ by ,minute degrees which tend to produce minute roughnesses on the sheets. Iiy the cable-drive herein described this is overcome.

The furnace may be heated in any desired manner. Heretofore most installations have employed gas, but my preference is to einploy electrical resistors mounted horizontally above and below the rolls as shown at 27 and 28 respectively in Fig. l. By the use of electrical heating and maintaining a slight positive pressure of a reducing atmosphere inside the furnace, combined with certain obvious precautions at the entrance and exit apertures, the annealed plates are delivered bright and polished.

` Even with fuel firing it is customary, however, to maintain a slight positive pressure inside the furnace to prevent entrance of outside air. In order to prevent escape of the hot gases through the roll shafts, which would have the multiple disadvantage of wasting heat from the furnace, overcooling the rolls, and overheating the bearings, the interior of each shaft is closed-olf in some manner. When the shaft is made solid as shown in Fig. 2 this takes care of itself, but when the shaft is made hollow as shown in Figs. land 8, the best plan is to close the inner end of the hole with a. plug 30 which may be either of metal or of refractory cement. Leakage ar-ound the exterior of the shaft is best prevented by a packing of some soft refractory material such as asbestos 31 held in place by a plate 32.

I do not limit myself to any one alloy although I prefer to use one containing between about 14% and about 18% of chromium together with from about 1/70 to about 2% of silicon and from about 30% to about 38% of a non-ferrous, iron-group metal, the balance consisting chiefly of iron, and the percentage of carbon beingpreferably kept very small. Such an alloy will readily withstand a temperature as high as 2250O Fahrenheit without deterioration; and most of the compositions within the range indicated are readily machined although this is not highly important to the present design since the rolls can be finished solely by surface grinding which renders many other alloys available for the purpose.

One advantage of all such alloys for the purpose in view is that their coefficient. of heat conductivity is rather small so that their tendency to become overheated at their ends is small, especially when the shafts are made hollow. This fact, coupled with the 'mounting of the bearings wholly outside the furnace and in heat conducting contact with an external metallic frame work of substantial dissipating area, keeps the temperature of the bearings down so low that I have been able to employ Babbitt metal bearings and lubricating oil without the use of local cooling even with a furnace temperature above 19000 F. In case a lower bearing temperature is desired I introduce into the hollow shaft a small water pipe 35 connected to a header 36. Only a slow vdrizzle is required in any case and it may be allowed to evaporate entirely; I do not find such water cooling generally necessary ,since the air cooling of the furnace frame coupled with the heat conductive mounting of the bearings constit-utes a sutlicient means to dissipate the comparatively small amount of heat which the peculiar construction 4of the roll allows to reach the bearing portion.

Rolls of the composition and construction herein described have been operated for a long time at temperatures above 2100*"- F. without observable deterioration or breakdown of any kind. Owing to the peculiar shape of the rolls and the method of mounting many alloys can be employed which would not exhibit the necessary physical strength in other designs. I have chosen sheet annealing as an example chiefly because this process constitutes a particularly dilhcult test of any furnace owing to the thinness of the product and the fact that the process must be performed without injury to the surface appearance. It is obvious that the furnace can be used for purpose of heating or reheating sheets, skelps, blooms, bars, rods, rails, plates, etc., before or during rolling and forging operations, and I believe myself to be the first to produce a furnace of this type where the rolls are operated at the full furnace temperature, wholly wit-hout cooling even up to intense white heats of 2200o F. I do not limit myself to the alloy mentioned nor to any details of design or structure except as specifically recited in my several claims, which I desire may be construed each independently of limitations contained in other claims.

Having thus described my invention what I claim is:

l. In a metallurgical furnace, a plurality of parallel horizontal one piece rolls traversing the furnace chamber and having coaxial shafts at opposite ends projecting through the furnace walls, each roll being hollow and larger than its shafts, and means for rotating all said rolls in the same direction at the same peripheral speed, said shafts having no passageway therethrough.

2. In a metallurgical furnace, a plurality of parallel, horizontal, metal rolls located in the furnace chamber and having coaxial `bearing portions at opposite ends thereof projecting through the furnace walls, a metallic frame work outside the furnace walls,

bearingsv foisaid 4bearing portionsy carried.

by said frame work, fsaidbearings Vhaving rheat conducting contact with said framework, 4meanswfor rotating .all said rolls, and

meal-)sier 4prever-ating the convection .of gasewillicht `is Aformed with a horizontal rowof spaced taper-ing apertures, each aperturev being larger. at its innerl end ,than` at its outer 'vend and the apertures inthe respective walls being opposite each other, a plu.-

raliity, ofl parallel, horizontal, .metal rolls. traversing the furnace chiunber and having their ends located inthe-:larger parts of. said apertures, eac-hof saidy rolls .having ateach end a coaxialrig-id shaft 0f smaller diameter than `thee-roll body, saidshafts projecting through thesinaller parts io1 said apertures, andameans outside 4'the furnace walls `for supporting andfdriv'ing said rolls, the body lportion of each .roll being externally cylindrical andi internallyhollow and having. perforaf tions between said shafts.

14. In a metallurgical furnace, a furnace body having spaced upright walls, Ieach of which is formedl with a.horizontal row of spaced\-alpe1ftures,.each aperture in one wall being opposite .an aperture in the other wall nndrhaving its inner 'en d; of* larger diameter than lits outer eend, a plurality of parallel, horizontal, hollow, perforated 4metal rolls traversingthe furnace chamber, each of said rolls having at each `end ahollow., integral, coaxial sha'zttfof smallery diameter.' vthan Vthe -rollz itselfl .and merging therewith by way offa flared portion, andbearings for said shafts outside the furnace wallyeachy rol] haring-.its flared :portions confined substantially withinrthe limits ofthe furnace walls.

5. Inl-a metallurgical furnace, .a plurality of: parallel horizontal, one piece` metal rolls `traversing v.the v'furnace body from side to side, the ends of said rolls being of.` reduced diameter to 'formshafts and the body thereof inside the furnace being of' enlarged; size 'to constitute the roll proper, bearings :for ythe yshwiitslocatedoutside o-fand spaced from hthe furnace walls, and vmeans for cooling the :eax osedKV portions locally, the walls ofv the :ro l'being thin whereby conductionliof heat to saidnshafts 'is reduced, and perforated whereby Vfternperattire. equalization 'is :facilita'ted. v

V6. In `a V*metallurgical diunnace, plurality oef parallel, horizontal, hollow metal rolls,

each .roll having a .bearing portion extending voutside off said furnace, bearings ttor said .roils'locaed outside fof said iurnace, means for heating that portionV of ythe interior. of

leacl'lf rolll` which liesinsde :the furnace to` .the

full, furnace temperature,I and` means for purevrenting .the .lowjo suclrheat ybyvil'ud convection .toward either end ,of` said roll..

7. In. a; yheat-treating furnace, y theL comlbijnation with` a.- plurality of parallel horizontal hollow .cylindrical perforated rolls adaptedy to convey the material, each roll beingnmade of metal andintegral fromy end to end, ,the end portions being of reduced 'size to consti# tute .bearing portions, of bearings for said hearing portions, and means for cooling said,l bearings locally, the cross. sectional area of the .metal being4 reduced adjacent to each end ofsaid roll sowas to restrict the rate of;- heat .flow from-'the body of thek roll to said hea-ring portions.

8. In a; furnace, ab plurality of parallel, horizontal, hollow, metal rolls having. integral cylindrical bearing portions at their ends, each roll having its bearing portions located outside oi' the fulfnfrleq. and vIHQELIIS for preventing fluid .movement between such bearing portions andthe hollow bodies of said rolls, while .peilnittiridgf` fluid movement between the interiors of :said bodies andthe furnace interior. Y

9. A roll fora heat-treating furnacevcomf prising .a .hollow cast -metal 'body 'having reducedv vintegral coaxiall end portions--vconstil tuting bearingshafts, 'and also having-per- .forations between saiclshats-` 10.` Al roll for a,V 'heat-treating 'furnace comprisinga hollow cast metal having reduced ,integral coaxialholilow end portions constituting bearing. shafts, .and also having perorations .betweemsaid shafts..

11. A. roll for` a lieat-.treatifurnace comprising aehollow. metal body laving V,reduced integral coaxial hollow end` ,portions constituting bearingsh'afts and plugs in the `inner ends of said shafts.

a2. A roll. for a heat-treating furnace comprising a hollow, substantially Qylindrf cal, metalbody having ateachend .a hollow portion of gradually .deoreasingwd-iameier which is formed. with apertures, andan integral -coaxialshaft at eachendnrith which `Such Vtapering portion merges,

1.3. A roll ,for a. heat-,treating furnace comprising .a hollow, substantiallyfcylindrical, `metal Ebody `having-a plurality of apar- Ytui-es therein, and .also .having at eachl enda ,tapering hollow .inte ral portionv which K merges into .a coaxial s iaft.

14. A roll for .a heat treatingv furnace -consistingof an [integrall casting 4hollpw from end to end and concentric :to .a vsingle, axis,

the end portions constituting Shafts, `the middle portionbeing `lof. increased diameterA and constituting-the- `roll body., the intermediate portious being;I tapered, said .body

having apertures-therein.

15. A roll. for furnaces comprising og1101 low @body off 4high .temperature *alloy` having terminalso reduced Size cvnstitutlrig'bearings, and closures between each bearing and the chamber defined within such hollow body whereby flow and convection of liuid is prevented.

16. A roll for furnaces comprising a hollow body of high temperature alloy having hollow axial terminals of reduced size constituting bearings, and means preventing passage of fluid between the interior of said body and the interiors of said bearings.

17. A cast metal roll which is made of high temperature alloy and hollow from end to end, its intermediate portion being larger than its end portions and its inner surface being everywhere substantially parallel to its external surface whereby its thickness is everywhere substantially uniform, and means preventing fluid communication between the larger and smaller portions of the 20 roll interior.

18. In a furnace of the character described, a plurality of non-cooled rolls of metal operatively mounted therein, said rolls having hollow bodies and hollow ends,

the interior of said bodies being in oommuniz.

cation with the furnace interior but not in communication with the interior of such ends.

19. In a furnace of the character described, non-cooled rolls of metal operatively mounted therein, said rolls having hollow, thin walled bodies traversing the furnace interior and having cylindrical bearing portions of reduced cross sectional area extending through and journaled outside of the furnace walls, and means preventing gas convection between portions which are inside and outside said furnace.

In testimony whereof l hereunto affix my signature.

FRANK A. FAHRENWALD. 

